Authorities placed all airports on red alert Thursday after a telephone caller warned of a suicide bomb threat to Islamabad's international airport, officials said.
Passengers were briefly evacuated from the capital's Benazir Bhutto airport while security officials searched the area, but all flights were operating as normal, they said.
"We have raised the security level to red alert. It was already on high alert but after the bomb threat in Islamabad we stepped it up," senior airport security force official told media.
In Islamabad, officials said security had been massively stepped up at the entrance and exit gates after a caller made a specific warning about an attack on the airport on Thursday.
"The airport received a telephone threat that a bomb could go off inside the building about midday," Islamabad airport official told media.
"Passengers were evacuated for a short time for debriefing on measures that security forces were taking because of the threat but then they were allowed to return. But there was no delay to flights," airport official said.
Road traffic to the airport was suspended for a short time.